Evidence for autophagy-dependent pathways of rRNA turnover in<i>Arabidopsis</i>

Floyd, Brice E.; Morriss, Stephanie; MacIntosh, Gustavo C.; Bassham, Diane C.

doi:10.1080/15548627.2015.1106664

Cited by 84 publications

(121 citation statements)

References 93 publications

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“…S1B). Similar defects were also observed in four individual YFP-ATG8e/atg9-3 transgenic lines and with another two independent ATG9 alleles, atg9-2 (26) and atg9-4 (16,17), as well as under a different autophagy inducer, DTT (Fig. S1 C-E).…”

Section: Atg9 Malfunction Results In Accumulation Of Abnormal Autophasupporting

confidence: 57%

“…Arabidopsis, an ATG9 counterpart has also been identified and shown to affect autophagic activity during starvation or pathogen infection (6,(15)(16)(17). To investigate the functional role of ATG9 in autophagosome formation in plant cells, we transformed the autophagosomal marker YFP-ATG8e into an ATG9-deficient mutant, atg9-3 (9).…”

Section: Atg9 Malfunction Results In Accumulation Of Abnormal Autophamentioning

confidence: 99%

“…atg7-2 (GABI_655B06) (15) T-DNA insertion mutant was obtained from the Nottingham Arabidopsis Stock Centre. atg9-4 (SALK_145980) mutant was as previously reported (16,17). Seeds were surface sterilized and sown on plates with Murashige and Skoog (MS) salts plus 0.8% agar.…”

Section: Methodsmentioning

confidence: 99%

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ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis

Zhuang

Chung

Cui

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

221

162

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Autophagy is a conserved pathway for bulk degradation of cytoplasmic material by a double-membrane structure named the autophagosome. The initiation of autophagosome formation requires the recruitment of autophagy-related protein 9 (ATG9) vesicles to the preautophagosomal structure. However, the functional relationship between ATG9 vesicles and the phagophore is controversial in different systems, and the molecular function of ATG9 remains unknown in plants. Here, we demonstrate that ATG9 is essential for endoplasmic reticulum (ER)-derived autophagosome formation in plants. Through a combination of genetic, in vivo imaging and electron tomography approaches, we show that Arabidopsis ATG9 deficiency leads to a drastic accumulation of autophagosome-related tubular structures in direct membrane continuity with the ER upon autophagic induction. Dynamic analyses demonstrate a transient membrane association between ATG9 vesicles and the autophagosomal membrane during autophagy. Furthermore, trafficking of ATG18a is compromised in atg9 mutants during autophagy by forming extended tubules in a phosphatidylinositol 3-phosphatedependent manner. Taken together, this study provides evidence for a pivotal role of ATG9 in regulating autophagosome progression from the ER membrane in Arabidopsis.O ne long-lasting question regarding autophagosome biogenesis is its membrane origin (1). The initiation site for autophagosomes is termed the preautophagosomal structure or phagophore assembly site (PAS). However, the source of the phagophore membrane remains controversial in different systems, and exactly how the phagophore is initiated from its membrane origin is still unclear. The core autophagy-related (ATG) machinery regulates phagophore assembly in a spatiotemporally coordinated manner whereas some of the ATG components will disassociate from the completed autophagosome and some are turned over together with the autophagosome (1-3).As the sole transmembrane protein, autophagy-related protein 9 (ATG9) has long been suggested to provide a lipid/membrane source for autophagosome formation because ATG9-deficient mutants in yeast or mammal fail to form autophagosomes (4, 5). Although ATG9 is conserved in all eukaryotes (6), it seems that ATG9 might perform its function divergently in different systems. In yeast, ATG9 participates in an early step by shuttling from a non-PAS site to the PAS site and supports an assembly model for yeast autophagosome biogenesis (4). In contrast, mammalian ATG9 is not stably incorporated into the isolation membrane or autophagosomes but is instead transiently associated with the omegasome, a phosphatidylinositol 3-phosphate (PI3P)-enriched endoplasmic reticulum (ER) subdomain (5). Cryomicroscopy studies have shown a close association between ATG9 vesicles and the omegasome structure (7), together with the presence of ATG9 on tubulovesicular membranes surrounding autophagosomes (5). A recent finding by livecell imaging indicates that autophagosome formation occurs where ATG9 vesicles coalesce with the ER ...

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Section: Atg9 Malfunction Results In Accumulation Of Abnormal Autophasupporting

confidence: 57%

Section: Atg9 Malfunction Results In Accumulation Of Abnormal Autophamentioning

confidence: 99%

See 1 more Smart Citation

ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis

Zhuang

Chung

Cui

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

221

162

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“…In this study, MRF deficiency accelerated rRNA degradation during DS, while MRF1 OE accelerated rRNA recovery during ReLG ( Figure 7D). We speculate that the translation defect by MRF deficiency under DS may lead to premature dissociation of the translating ribosomes or stalled ribosomes, which then become a target for degradation via cytosolic ribonucleases, ribophagy, or both (Zundel et al, 2009;Floyd et al, 2015). In contrast, MRF1 OE may boost mRNA translation during ReLG, resulting in faster rRNA recovery.…”

Section: Discussionmentioning

confidence: 95%

MRF Family Genes Are Involved in Translation Control, Especially under Energy-Deficient Conditions, and Their Expression and Functions Are Modulated by the TOR Signaling Pathway

et al. 2017

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Dynamic control of protein translation in response to the environment is essential for the survival of plant cells. Target of rapamycin (TOR) coordinates protein synthesis with cellular energy/nutrient availability through transcriptional modulation and phosphorylation of the translation machinery. However, mechanisms of TOR-mediated translation control are poorly understood in plants. Here, we report that Arabidopsis thaliana MRF (MA3 DOMAIN-CONTAINING TRANSLATION REGULATORY FACTOR) family genes encode translation regulatory factors under TOR control, and their functions are particularly important in energy-deficient conditions. Four MRF family genes (MRF1-MRF4) are transcriptionally induced by dark and starvation (DS). Silencing of multiple MRFs increases susceptibility to DS and treatment with a TOR inhibitor, while MRF1 overexpression decreases susceptibility. MRF proteins interact with eIF4A and cofractionate with ribosomes. MRF silencing decreases translation activity, while MRF1 overexpression increases it, accompanied by altered ribosome patterns, particularly in DS. Furthermore, MRF deficiency in DS causes altered distribution of mRNAs in sucrose gradient fractions and accelerates rRNA degradation. MRF1 is phosphorylated in vivo and phosphorylated by S6 kinases in vitro. MRF expression and MRF1 ribosome association and phosphorylation are modulated by cellular energy status and TOR activity. We discuss possible mechanisms of the function of MRF family proteins under normal and energy-deficient conditions and their functional link with the TOR pathway.

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“…Down-regulation or depletion of RPL37 is a well-established inducer of ribosomal stress, which has been shown to decrease MdmX protein levels and activate p53 [36–38]. Ribosomal stress induced autophagy has been reported in Arabidopsis [39] and yeast [34]. In eukaryotic cells, autophagy probably contributes to the proteome turnover while protecting the degradation of ribosomes [40].…”

Section: Discussionmentioning

confidence: 99%

Role of microRNA-4516 involved autophagy associated with exposure to fine particulate matter

Hao

et al. 2016

Oncotarget

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Metals are vital toxic components of fine particulate matter (PM2.5). Cellular responses to exposure to PM2.5 or PM metal components remain unknown. Post-transcriptional profiling and subsequent cell- and individual-based assays implied that the metal ion-binding miR-4516/RPL37/autophagy pathway could play a critical role in cellular responses to PM2.5 and PM metal stresses. miR-4516 was up-regulated in A549 cells exposed to PM2.5 and in the serum of individuals living in a city with moderate air pollution. The expression levels of the miR-4516 target genes, namely, RPL37 and UBA52, were involved in ribosome function and inhibited by exposure to PM2.5 and PM metal components. Autophagy in A549 cells was induced by PM2.5 exposure as a response to decreased RPL37 expression. Moreover, enhanced miR-4516 expression was positively correlated with the augmentation of the internal burden of aluminum and lead in individuals living in a city with moderate air pollution. Hereby, the miR-4516/RPL37/autophagy pathway may represent a novel mechanism that mediates responses to PM metal components.

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Evidence for autophagy-dependent pathways of rRNA turnover inArabidopsis

Cited by 84 publications

References 93 publications

ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis

ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis

MRF Family Genes Are Involved in Translation Control, Especially under Energy-Deficient Conditions, and Their Expression and Functions Are Modulated by the TOR Signaling Pathway

Role of microRNA-4516 involved autophagy associated with exposure to fine particulate matter

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